MONDAY, May 13 (HealthDay News) -- The next time you sit down at your favorite local eatery, ponder this: Two new studies find that the average restaurant meal provides diners with most of the calories, fats and salt they require for the entire day.

The authors of both reports said these excesses can make restaurants unhealthy places to eat, adding to the obesity epidemic and increasing diners' risk for heart disease.

"In all of the meal categories there are huge ranges in calories, sodium and fats," said Mary Scourboutakos of the University of Toronto, and lead author of one of the studies. "You really don't know [what menu choice is healthiest] unless there is calories labeling or sodium labeling. There is no way to predict which meals are going to be the worst."

Both reports were published May 13 online in JAMA Internal Medicine.

The first report was conducted by researchers from the Human Nutrition Research Center on Aging at Tufts University in Medford, Mass. They found that most typically ordered restaurant meals contain more than half the calories the person would need per day.

"Your average serving -- just an entree, no drinks, no appetizers, no desserts -- is virtually a whole day's calories on one plate," said lead researcher Susan Roberts, director of the center's Energy Metabolism Laboratory.

For the study, Roberts' team analyzed 157 full meals from 33 restaurants in the Boston area.

They found 73 percent of the meals ordered had over half of the 2,000 daily calories recommended for adults by the U.S. Food and Drug Administration, and 12 meals contained more than the full daily recommendation.

Large portion sizes seemed key, the Boston study found, because prior research has shown that people tend to eat what is placed in front of them.

"When restaurants provide these [large] portions -- which are far more than the human body can process -- they are very directly contributing to the terrible epidemic of obesity we have today," Roberts said.

Meals with the highest average number of calories included those from restaurants specializing in Italian (1,755 calories), American (1,494 calories) and Chinese (1,474 calories) fare. Meals with the fewest average number of calories were from Vietnamese (922 calories) and Japanese (1,027 calories) restaurants, the researchers said.

A person's local diner or family-run restaurant was just as likely to pile on the calories as a big chain, the Boston study found. In fact, local, small-chain restaurants tended to have slightly higher calorie counts per meal (an average of 1,437) than national chains (1,359), although the difference wasn't statistically significant.

However, without the aid of calorie counts on menus, figuring out which meal is better for you can be tough.

Without posted calorie counts, there was "no way to identify the meals that had appropriate calories for a normal human being," Roberts said. "Portions and calories per ounce were very variable between restaurants even for the same dishes -- often by a factor of two."

Therefore, "restaurants that do not provide nutrition information are very unhealthy places to eat, from the calorie perspective," she said. Roberts would like to see many more restaurants posting calorie and nutrition information, "so consumers can choose whether to overeat or not."

In the second study, Canadian researchers led by graduate student Scourboutakos analyzed 685 meals and 156 desserts from 19 sit-down, chain restaurants.

They found the average breakfast, lunch and dinner contained 1,128 calories, again a majority of the daily number of calories recommended for adults.

In addition, the meals typically contained 151 percent of the daily amount of salt a person should ingest daily, 89 percent of the fat recommended per day, 83 percent of daily recommended saturated and trans fats, and 60 percent of the cholesterol one should have daily.

One expert agreed that restaurant meals often include unexpected amounts of calories, salt and fat.

"Eating out is fun," acknowledged Samantha Heller, a senior clinical nutritionist at New York University Medical Center in New York City. "For the homemaker, it is a break from nightly cooking and cleaning up." However, the problem is that many, if not most, restaurant foods, whether from chain or local eateries, contain far more saturated fat, calories and sodium than anyone would imagine, she said.

"Recently, I reviewed online menu choices from a chain restaurant with a patient. The grilled chicken salad he was eating regularly and believed was a healthy choice, wound up having over 2,000 milligrams of sodium and 41 grams of fat. He was stunned," she said.

Another problem is that many people eat out several times a week, putting them at risk for overeating, Heller said.

The good old family meal has advantages beyond a healthy diet, she noted. "Family meals at home keep kids healthier and support better relationships among family members, reduce disordered eating and substance abuse and improve well- being," Heller said. "If you eat out several times a week, try cutting back a few nights. Fresh, home-cooked meals can be simple, healthy and delicious."

Another study published in the same journal found that much-touted voluntary reductions in salt levels in foods by the restaurant and food industry has been "inconsistent and slow."

The research, led by Michael Jacobson from the Center for Science in the Public Interest (CSPI) in Washington, D.C., found that salt in 402 processed foods dropped by only about 3.5 percent from 2005 to 2011.

Over the same period, the amount of salt in fare from 78 fast-food restaurants rose by 2.6 percent.

While some food products saw a 30 percent decrease in salt, more saw at least a 30 percent increase, the CSPI researchers found.

"Stronger action [for example, phased-in limits on salt levels set by the federal government] is needed to lower sodium levels and reduce the prevalence of hypertension and cardiovascular diseases," the researchers concluded.